Edit:
Forgot one of the wierdest ones, where the nights watch apparently swore allegiance to Mance Rayder, and fought as his bannermen against the Iron Throne. Once he was defeated, the watch returned to its normal, independant state.
Playing as Robb Stark, I had a CB to go to war with the wildlings to "restore the Night's Watch". Seemingly, Mance (or his heir) can take over castle black, usurp the title of night's watch and inherit their troops. You have to fight to re-establish them.
One thing with the Night's Watch i don't understand... I never saw their troops once while playing as Robb. I fought off 6-7 invasions from beyond the wall (no big deal, they bring like 2k troops) but wtf is the Watch doing if they're not preventing invasions from beyond the wall?
Also, you get past castle black faster than some of the territory in the Vale... how is that even possible?